Implantable medical devices (IMDs), including pacemakers and implantable cardioverter-defibrillators (ICDs), record cardiac electrogram (EGM) signals for sensing cardiac events, e.g., P-waves and R-waves. Episodes of bradycardia, tachycardia and/or fibrillation are detected from the sensed cardiac events and responded to as needed with pacing therapy or high-voltage cardioversion/defibrillation therapy. Reliable detection and treatment of potentially life-threatening ventricular tachycardia (VT) and ventricular fibrillation (VF) requires reliable sensing of cardiac signals.
Dislodgement or dislocation of a cardiac lead carrying electrodes for sensing EGM signals reduces reliable sensing and could result in erroneous sensing of cardiac signals, leading to improper detection of the cardiac rhythm and inappropriate delivery or withholding of pacing or shock therapy. While an occurrence of ventricular lead dislodgement is rare, such dislodgement could potentially cause inappropriate shock therapy to be delivered. For example, in some rare instances of a ventricular lead dislodging or being dislodged during an episode of sinus tachycardia or atrial fibrillation, atrial cardiac signals associated with the episode may be inappropriately sensed as ventricular signals, causing inappropriate detection of a ventricular fibrillation episode and the resultant delivery of high-voltage anti-tachyarrhythmia therapy. In some cases, a dislodged lead may cause a necessary or optimal therapy, such as bradycardia pacing, anti-tachycardia pacing, or anti-tachyarrhythmia shock, to not be effective because the therapy electrodes moved from the implanted location. Accordingly, it is desirable to provide an implantable medical device and associated medical device system that is capable of detecting ventricular lead dislodgement.